Carbon dioxideerodes marineecosystemsResearch suggests how sealife will react to acidification

By Janet Raloff

If carbon dioxide emissions don’t begin
to decline soon, the complex fabric
of marine ecosystems will begin fraying — and eventually unravel completely,
two new studies conclude.

The diversity of ocean species thins
and many survivors’ health declines as
the pH of ocean water falls in response
to rising carbon dioxide levels, scientists from England and Florida reported
February 18. What’s more, affected
species aren’t restricted to those with
shells and calcified support structures — features particularly vulnerable
to seawater acidification.

Jason Hall-Spencer of Plymouth University in England and his colleagues
have been collecting data from marine
sites off Italy, Mexico and Papua New
Guinea, where high concentrations of
carbon dioxide percolate out of the sea-bed from volcanic activity below. Directly
above these CO2 seeps, pH plummets to
7. 8 or below, a value that is expected to
occur widely by 2100 and which is substantially lower than the normal level for
these areas, 8. 1. The sites offer a preview
of what may happen to seafloor ecosystems as CO2 levels continue to rise.

Compared with nearby normal-pH
sites, species richness in low-pH zones
was diminished by 30 percent, Hall-Spencer reported. “Coral and some algae
are gone. And the sea urchins are gone,”
he said. Fish may be present, but unlike
in areas with a normal pH, they won’t
deposit their eggs there.

Although seagrasses appear to survivejust fine in the low-pH seawater, closeinspection showed that fish had nibbledthe fronds, Hall-Spencer found. He iden-tified one likely explanation: At low pH,these grasses no longer produced thephenolic defense compounds that typi-cally deter grazing animals.